Despite Robert DeNiro seemingly being a bit more consistent over the years, with a few more great films to his name, I've always stuck with Pacino as my favorite actor and, in my opinion, the best of all time.

The Godfather
The Godfather Pt II
Heat
Donnie Brasco
Scent of a Woman
Scarface
Carlito's Way
Insomnia
Dog Day Afternoon

just some of my favorites of his.